1. Field of the Invention
The invention relates to a manufacturing method of a battery pack that includes a plurality of single cells each having an electrode body that includes an electrode plate and a separator, and a restraining member that restrains the single cells.
2. Description of Related Art
A battery pack is known in which a plurality of single cells are stacked directly or alternately via spacers, and the restrained by a restraining member.
Normally, when a battery Pack is assembled, the assembled single cells are supercompressed in the stacking direction beforehand to improve workability. This is because workability is improved when the single cells are restrained by a restraining member or the like, as a result of the dimension (thickness) of the single cells being reduced beforehand by supercompressing them. More specifically, in a battery pack in a complete state, the highest maximum contact pressure, of pressure that is applied in the thickness direction of the separator and the electrode plate that form the electrode body housed in the single cells by the restraining member and is distributed in the spreading direction of the separator and the electrode plate, is the maximum restraint contact pressure. After the single cells are supercompressed at a compression contact pressure that is sufficiently larger than this maximum restraint contact pressure, for example, several times larger than the maximum restraint contact pressure, the battery pack in which these supercompressed single cells are restrained by the restraining member is assembled. Finally, an adjustment is made such that the maximum restraint contact pressure is applied to each of the single cells while the battery pack is in the complete state.
As described in Japanese Patent Application Publication No. 2001-236985 (JP 2001-236985 A), it is expected that when conductive foreign matter present in the electrode body of a single cell is large enough to possibly cause a short when the battery pack is stored or used in the future, this foreign matter may pass through the separator when the single cell is supercompressed at the compression contact pressure, and a positive electrode plate and a negative electrode plate of the single cell may become electrically connected via this foreign matter, causing a short. Therefore, with such a battery, it is conceivably possible to differentiate a single cell in which a short may occur by a test in a short period of time and remove the single cell.
However, it is now known that when conductive foreign matter is small, a short will not occur in the future even if such small foreign matter is present in the electrode body, even if the maximum restraint contact pressure described above continues to be applied. However, if the compression contact pressure described above is too high, even if the conductive foreign matter is small, it will damage the separator. It is also know known that if an extended period of time passes while the battery pack is in a state in which the maximum restraint contact pressure is applied to such damaged single cells (i.e., if the single cells that are damaged in this way continue to be restrained by the restraining member at the maximum restraint contact pressure), the foreign matter may pass through the separator, and the positive and negative electrode plates may become electrically connected via this foreign matter, causing a short. However, to eliminate this, a short circuit test must be performed for an extended period of time after the battery pack is assembled, which is unrealistic.